Abstract: The cause of subway station top floor cracking during construction is analyzed, and the tempera- ture stresses ofthe monitoringsection are computed usingthe practical test data. It is pointed outthat during construction the hydration heat will not cause the subway station top floor to crack, and that in designing structures of the same kind, it is unnecessary to design the after-pouring construction joint. On the other hand, using cement of low hydration heat or decreasing the amount of cement is important.